7
Mfr. code
10x-1-100
Pin 1
a. 10
Ω
Resistor Network
Mfr. code
10x-1-106
Pin 1
b. 10 M
Ω
Resistor Network
Figure 3.
Resistor Networks
Open-Thermocouple Detection
The VXI-TB-1303 circuitry helps you detect an open thermocouple.
To detect whether any thermocouple is open, check whether the
corresponding VXI-SC submodule channel is saturated. The
VXI-TB-1303 has pull-up and ground-reference resistors that saturate
the channel by ap5 V at the input of the open channel. This
will cause saturation to either of the positive or negative rails.
VXI-SC-1102 Submodule
With the 10 M
Ω
ground-reference resistor networks, it does not matter
whether your signal is ground-referenced or floating. The channels with
open thermocouples will saturate at all sample rates of the submodule.
Errors Due to Open-Thermocouple Detection Circuitry
Open-thermocouple detection circuitry can cause two types of
measurement errors. These errors are caused by common-mode voltage
at the input of the VXI-SC submodule and current leakage into your
signal leads.
Common-Mode Voltage at the Input of the VXI-SC
Submodule
With 10 M
Ω
pull-up and ground-reference resistor networks, a
common-mode voltage of 2.5 VDC will develop if the thermocouple
is floating. At a gain of 100, the common-mode rejection of the
VXI-SC-1102 submodule is sufficiently high that the resulting offset
voltage is negligible.
